1. Field of the Invention
The present invention relates to a modified layer forming method of applying a pulsed laser beam having a transmission wavelength to a workpiece in the condition where the focal point of the pulsed laser beam is set inside the workpiece, thereby forming a modified layer inside the workpiece.
2. Description of the Related Art
There is in practical use an internal processing technique of applying a pulsed laser beam having a transmission wavelength to a transparent or translucent workpiece in the condition where the focal point of the pulsed laser beam is set inside the workpiece, thereby forming a modified layer inside the workpiece to create a pattern, figure, or character (see Japanese Patent Laid-open No. Hei 7-76167, for example).
There is also in practical use an internal processing technique of applying a pulsed laser beam having a transmission wavelength to a wafer such as a silicon wafer and a sapphire wafer along a plurality of crossing division lines partitioning a plurality of devices such as ICs, LSIs, and LEDs formed on the front side of the wafer, in the condition where the focal point of the pulsed laser beam is set inside the wafer, thereby forming a modified layer as a division start point inside the wafer along each division line (see Japanese Patent No. 3408805, for example).